This invention relates to a high-speed commmunication system and, more particularly, to an optical time-division-multiplex system.
In recent years, as the demand for higher-capacity communication systems has proliferated, the use of optical fibers as the transmission medium in such systems has significantly increased. The attractiveness of such a medium is based on the recognition that the bandwidth of a single-mode optical fiber channel is in the teraHertz range (10.sup.12 signals per second).
In a typical system in which an optical fiber is employed to interconnect electronic circuitry in a transmitter to electronic circuitry in a receiver, the electronic circuitry as heretofore realized is usually not capable of operating at speeds in the teraHertz range. Thus, for example, by way of an example, for a fiber carrying signals at a one-teraHertz rate, the electronic circuitry associated therewith is capable in practice of operating at only at best a 125-gigaHertz rate.
Accordingly, various multiplexing techniques (at the transmitter) and demultiplexing techniques (at the receiver) have been proposed to interface relatively low-speed electronic circuitry to high-speed fibers. In, for example, a so-called time-division-multiplex (TDM) system, multiple low-speed signal sequences at the same rate are interleaved and applied to a fiber as a single high-speed serial sequence. Thus, illustratively, by interleaving eight 125-gigaHertz signal sequences, it is feasible to utilize a one-teraHertz fiber with electronic circuitry at the transmitter and receiver capable of operating at only 125 gigaHertz. In such a system, individual signals from eight different channels are transmitted in sequence in an alternating fashion.
Heretofore, the problem of demultiplexing or distributing the interleaved optical signals propagated in a high-speed fiber in a TDM system has proven to be a formidable one. Electro-optic deflectors, for example, have been suggested for use at the receiver of a TDM system for deflecting and thereby routing successive received signals to respectively different photodetectors. But achieving electro-optic deflection in the teraHertz range is an extremely difficult, if not currently impossible, task. Also, the materials utilized in practice to realize electro-optic deflectors are typically different than the silicon-based materials commonly employed to make photodetectors and other standard components of the receiving circuitry. As a result, integrating such deflectors with the other circuitry on a single receiver chip is not easily realized using conventional batch-fabrication integrated-circuit processing techniques.
Still other approaches have been suggested for demultiplexing a stream of high-speed optical signals in a TDM system. (A review of various TDM techniques is contained in an article entitled "All-Optical Network Consortium-Ultrafast TDM Networks" by R. A. Barry et al, IEEE Journal on Selected Areas in Communications, vol. 14, No. 5, June 1996, pages 1000-1013.)
But these other known proposed solutions also are characterized by serious drawbacks such as extreme complexity, speed-limited capability (relative to the one teraHertz range) or lack of integratability on a single receiver chip.
Accordingly, continuing efforts have been directed by workers skilled in the art aimed at trying to provide an improved way of demultiplexing a high-speed optical signal sequence in a TDM system. It was recognized that such efforts, if successful, could provide a basis for enhancing the operation and lowering the cost of high-speed optical communication systems.